This invention relates to a developing device and an image forming apparatus.
In a conventional electrophotographic image forming apparatus (for example, a printer, a copier, a facsimile machine, a complex machine or the like), a surface of a photosensitive drum is uniformly charged, and the surface of the photosensitive drum is exposed with light to form a latent image thereon. The latent image is developed with toner adhering to the latent image by electrostatic attraction, so that a toner image is formed on the photosensitive drum. The toner image is transferred to a recording sheet, and then fixed to the recording sheet, with the result that the toner image is formed on the recording sheet.
An arrangement for forming the toner image on the photosensitive drum is integrated into a developing device. The developing device is detachably attached to a main body of the image forming apparatus such as a printer. The developing device includes a toner cartridge that stores the toner. The toner cartridge is detachably attached to a main body of the developing device.
FIG. 12 is a plan view of a main part of a conventional developing device.
In FIG. 12, a developer storing chamber 24 is formed in a main body of a developing device, and stores the toner. First and second developer carrying members 28 and 29 are disposed in the developer storing chamber 24. The second developer carrying member 29 faces a developing roller 31. A partition plate 32 is disposed between the first and second developer carrying members 28 and 29, and extend in the direction parallel to the axes of the first and second developer carrying members 28 and 29. The developer storing chamber 24 is divided by the partition plate 32 into first and second chambers C1 and C2. The first and second chambers C1 and C2 are connected to each other at end portions 24a and 24b respectively formed adjacent to both ends of the partition plate 32.
The toner is supplied to the developer storing chamber 24 through a supply port 25 formed at the end portion 24a of the developer storing chamber 24. Then, the first developer carrying member 28 carries the toner in the direction shown by an arrow “a” from the end portion 24a to the other end portion 24b of the developer storing chamber 24. The second developer carrying member 29 carries the toner in the direction shown by an arrow “b”, from the end portion 24b to the end portion 24a of the developer storing chamber 24. Further, the first developer carrying member 28 again carries the toner in the direction shown by the arrow “a” from the end portion 24a to the end portion 24b. 
With such an arrangement, the toner is carried by the developer carrying members 28 and 29 in both directions “a” and “b” and circulate in the developer storing chamber 24, so that the evenness of the distribution of the toner can be improved.
If the toner stays at one of the end portions 24a and 24b, the distribution of the toner becomes uneven. Therefore, the amount of the toner carried by the developer carrying members 28 and 29 are set to be different from each other, as disclosed in Japanese Laid-Open Patent Publication No. 9-146352.
However, in the conventional developing device, even if the amount of the toner carried by the developer carrying members 28 and 29 are different from each other, it is difficult to sufficiently improve evenness of the distribution of the toner, and therefore it is difficult to prevent the agglomeration of the toner at the end portion 24a or the end portion 24b. 
If the toner is agglomerated at the end portion 24a or the end portion 24b of the developer storing chamber 24, a stain, fog or the like may be generated at an end portion of the recording sheet. Moreover, the density of the toner at the center of the developer storing chamber 24 may decrease, and therefore an image blurring may be caused at the center portion of the recording sheet. Furthermore, there is a difference between charges of the toner (adhering to the developing roller 31) at the end portions and at the center portion, and therefore the unevenness of the image density may occur.
As a result, the quality of the image may be degraded.